Piston type hydrostatic power units



' H. THOMA 8 PISTON TYPE HYDROSTATIC POWER UNITS Filed June 27, 1960Oct. 8, 1963 2 Shet-Sheet 1 Hans Thoma. INVENTOR.

BY QZZ W Oct. 8, 1963 H THOMA 3,106,138

PISTON TYPE HYDROSTATIC POWER UNITS Filed June 27, 1960 I 2 Sheets-Sheet2 Hans Thoma. uvmvron BYJZZLWQAZ K United States Patent 3,106,138 PISTONTYPE HYDROSTATIC POWER UNITS Hans Thoma, Rotfluhstrasse 10, Zollikon,Zurich, Switzerland Filed June 27, 1960, Ser. No. 39,183 13 Claims. (Cl.92-156) This invention relates to piston type hydrostatic power unitsparticularly such units in which pistons operate or are operated by arockable shoe arranged between the outer ends of the pistons and anabutment such as a swash-plate, such as is shown, for example, in US.Patents 1,710,567, 1,945,391 and 2,093,477 or a ring as in US. Patent1,954,853.

Hydrostatic axial piston units are known, in which the outer ends ofpistons, operating in cylinder bores in a cylinder block in exactly orsubstantially parallel relationship to the axis of the cylinder block,carry a joint ball which has a rockable shoe which bears against aswash-plate which is usually fixed but which sometimes co-rotates at theaverage circumferential speed of the individual pistons and shoes.Hydrostatic radial piston units are also known in which the outer endsof pistons operating radially in cylinder bores in a rotor are eachprovided with a rockable shoe which bears against a driving ring whichis fixed or co-rotates at the average circumferential speed of theindividual pistons.

In such constructions, whether of the axial or radial type, aconsiderable lateral pressure is produced between the piston and thecylinder walls, especially near the outer ends of the cylinder bores,and this causes difficulty, especially at high speeds. According to theinvention, this lateral pressure which, in known constructions, is to beinterpreted as a mechanical load similar to that occurring in the caseof a crosshead, together with its wear and heating phenomena is to beobviated according to the present invention by supporting this lateralpressure by means of controlled pressure oil areas.

It is, therefore, an object of the present invention to provide conduitmeans for supplying oil under pressure between the pistons and cylinderwalls in those areas where lateral pressure between them is developedduring operation.

Another object is to provide valve means in said conduit means soarranged :as to supply oil under pressure only to those areas which atthe time are under lateral pressure.

Another object is to provide valve means in said conduit means actuatedas an incident to the rocking of the piston shoe relative to the pistonin such a manner as to supply oil under pressure only to those areaswhich at the 1 outer end of the cylinder and at the opposite side of thepiston near the inner end of the piston.

Another object is to so construct the pistons and the piston shoes as toadmit no oil to said conduit means when the shoe is co-axial with thepiston and to supply oil under pressure to one or more conduitsterminating at the shoe to one side of the axis While not supplying oilto the other conduits terminating at the other side of the piston axis.

Further objects and advantages of this invention will be apparent fromconsideration of the specification as illustrated by the accompanyingdrawings of possible em bodiments of the invention, in which drawings:

FIG. 1 is a partial cross-sectional view of a piston type hydrostaticpower unit illustrating one form of embodiment;

FIG. 2 is a partial enlarged cross-sectional view of the 3,l ,l38Patented Get. 8, 1963 "ice lower end of the piston of FIG. 1, the axialtube 8 being, however, shown in elevation;

FIG. 3 is a top view of the piston of FIG. 1;

FIG. 4 is an elevational view of the piston of FIG. 1;

FIG. 5 is an axial cross sectional view of a piston and piston shoe,illustrating a modified form of construction; and

FIG. 6 is a top view of the piston of FIG. 5, shown on an enlargedscale.

Referring to said drawings, 1 indicates one of the pistons of an axialpiston hydrostatic power unit which may be used either as a pump orhydraulic motor. Said piston is reciprocable in cylinder bores in acylinder block 2. Each cylinder is provided with a cylinder port 3cooperating with the usual kidney shaped valve ports in the valve plate4, connected respectively to the intake and delivery conduits.

The outer end of the piston is formed with the sperical ball 7 which islocated in a spherical socket in the piston shoe 7a which .is slidableon the abutment ring or swash-plate 7b. The shoe 7a may be held againstthe ring 7b by the usual spider 7c.

Piston 1 is formed with an axial bore 5 within which is tightly pressedthe conduit rod 8. As shown, the latter is formed with a plurality ofhelical grooves 18 (6 being shown), the outer end of which groovesterminate in the surface of the ball 7. 15 indicates transverse ducts inthe piston (6 being used in the form shown). The outer ends of thesebores 15 may communicate with oil distribution grooves 15 (FIGS. 1 and4). It will be noted that the pitch of the helical grooves 18 is sochosen that a half turn around the rod 8 is made from the upper end ofthe rod to the several ducts 15. The lower end of rod 8 is preferablyenlarged as at 17 and is preferably also formed with an enlargedthreaded head 17a engaged with threads in the piston. When the rod 8 isscrewed in place an oil type connection is formed between theenlargement 17 and the piston, preferably with the 'aid of a gasket. 9indicates a central bore in the rod 8 which bore terminates in line withtransverse ducts 10 in rod 8. 11 indicates transverse ducts in thepiston which open into circumferential groove 12 which communicates withthe space between the piston and the cylinder wall a short distance fromthe inner end of the piston. If desired, the end of the piston may bemade slightly smaller in diameter to permit oil at suflicient pressureto enter the ducts 11. The space betweenthe piston and cylinder wall isso small that only filtered oil can :enter ducts 11. The oil flowsthrough ducts 11 and 10 into bore 9 and into the pocket 14 in the shoe7a. From said pocket, the oil may pass through duct 14a into a pocket14b in the face of the shoe to lubricate and hydraulically balance theshoe 7a on the swash-plate ring 7b. When the shoe 7a is coaxial withpiston 1, as when the swash-plate 7b is perpendicular to the pistons, nooil can enter ducts 18. However, when the shoe is tilted 'as shown inFIG. 1, pressure oil in the pocket 14 enters that helical groove 18which starts the farthest to the left in FIG. 1, passes down said groovehalf way around the rod 8 and enters the duct 15 on the opposite side ofthe piston, through which duct it flows into the space between thepiston and the cylinder wall. If the tilt of shoe 7a is sufiicient orthe diameter of pocket 14 is made sufficiently large, oil may also enterone or two adjacent grooves 18 and pass therethrough to the adjacentducts 15 (not shown). It will therefore be seen that oil under pressureis led from the cylinder space below the piston through the ducts 11 and10, bore 9, pocket 14 and one or more grooves 18 to one or more ducts 15and distributed on that side of the piston where the lateral pressureoccurs.

The helical grooves 18 are preferably made very fine so as to provide athrottling effect. This aids in the automatic pressure balancing so asto provide only enough oil pressure between the piston and the cylinderwalls to separate them slightly, whereby excess oil leakage is avoided.

Transverse contact pressure also occurs at the inner end of the pistonon the side opposite to the point where the pressure is exerted at theouter end of the cylinder bore. While this pressure is less, it may becounterbalanced by continuing the helical grooves 18 (as shown) to apoint in line with the six transverse ducts 16. As shown, the helicalgrooves make a half turn in the distance between the ducts 15 and theducts 16 so that any groove 18 which supplies oil to the duct 15 on oneside of the piston will also supply oil to the duct 16 on the other sideof the piston. This is easily accomplished by making the distance fromthe upper end of rod 8 to the ducts 15 the same as the distance from theducts 15 to the ducts 16. If this is not convenient a variable pitchhelical groove may, of course, be employed. The oil may be spread to anyextent desired by providing oil distribution grooves 16' (FIGS. 1 and4). Furthermore, helical grooves may be formed on the inner surface ofthe bore 5 similar to grooves in a rifle barrel, in which event theexterior of the rod 8 may be smooth.

Another form of construction is illustrated in FIG. 5 in which thepiston 1a is formed with a central bore 5' within which is pressed thecentral conduit rod 8a, formed with external grooves 18a which terminateat their inner ends in ducts 15a which may be formed with oildistribution grooves 15'. The upper end of the rod 8a is formed with aconical head having grooves 24 herein which constitute a continuation ofgrooves 18a. If preferred, 24 may be drilled holes in the piston ball 7.In this form, controlled pressure oil areas at the inner end of thepiston are not provided. Throttling grooves 20 are shown formed in thepiston surface to permit pressure oil from the cylinder to balance thetransverse pressures at the inner end of the piston. The piston is shownprovided with an annular groove 22 communicating through bore 23 withthe exterior. Pressure oil may pass through the central bore 9a in therod 8a to an oil pocket 912 at its upper end and thence through duct 14ato a pocket 14b in the face of the shoe 7a. The shoe is shown formedwith an annular groove 26 connected by one or more ducts 27 to thepocket 1412', which as stated is supplied with high pressure oil throughbore 9a. The radius of the groove 26 is such with respect to the groovesor bores 24 that when the shoe 7a is perpendicular to the piston nocommunication occurs between 26 and 24. If, however, the shoe isinclined leftward, as shown in FIG. 5, pressure oil may flow fromannular groove 26 through duct 24, groove 18a and duct 15a to the oildistribution groove 15' at the right side of the piston. In this way, anoil pressure area is formed at the proper side of the piston to relievethe transverse pressure developed there. This form of construction hasthe advantage over that shown in FIGS. 1, 2, 3 and 4 in that it issomewhat simpler because it is not necessary to form helical grooves andstraight fluting may be used. It will also be noted that instead ofproviding the co-axial conduits as grooves on conduit rod 8a (or withinthe bore 5') the rod 8a may be dispensed with and the conduits 18a maybe formed as holes drilled in through the ball 7 If it is also desiredto provide balancing oil pressure areas at the bottom end of the piston,this can be accomplished by continuing the fluting in a helical form for180 degrees to the lower end of the correspondingly lengthened rod 8awhere ducts such as ducts 16 of FIGS. 1 and 2 would be provided.

The invention may be applied equivalently to axial piston pumps andmotors having inclined cylinder axes, which constitute as it were atransition to the radial piston pump or motor construction, and also toradial piston pumps or motors having a shoe adjustable at an angle orsimilar structural elements at their outer piston end. Whether the shoehas plane, cylindrical or spherical surfaces externally is obviouslyirrelevant to the invention. In the case of a pure radial pistontransmission, the spherical member illustrated at the outer piston endin the accompanying drawings may be replaced by a cylindrical elementwhich is connected to a corresponding shoe, or else these pistons may beprovided with an external cylindrically drilled bushing which isconnected to a cylindrical member which is in turn disposed on the shoe.In that case, the valving of the pressure oil sections would be effectedin the piston itself or else in an assoicated crosshead instead of thespherically movable surfaces in the corresponding cylindrical slidesurfaces. The valving would then proceed in a single plane, so that itwould be sufiicient to have two alternately pressurized relievingsurfaces on the piston with their pressure oil supply for the latter, orthe corresponding arrangement on a crosshead.

t is also possible to provide a crosshead in known manner on the outerpiston end in the case of the axial piston transmission as well, inorder to use its slide surfaces or the relieving thereof for thearrangement according to the invention. In these and in other cases itis also possible to replace the ball head of the pistons shown in FIG-URES l, 3, 5 and 6 by a ball cup which surrounds a ball element which inturn is connected to a slide shoe. In this case too the describedexpedients of slidable valving apertures in the correspondingcooperating slide surfaces obviously permit the automatic control inaccordance with the invention of the pressure oil areas on the piston orcrosshead, only insignificant structural modifications being required incomparison with the exemplified embodiments illustrated in the drawings.

The invention is not intended to be limited to the several illustrativeforms shown and described which are to be understood as illustrativeonly and not as limiting, as various changes in construction andarrangement may be made, including combining features of the said forms,all coming within the scope of the claims which follow.

I claim:

1. A hydrostatic power unit of the type having a piston reciprocating ina cylinder and a force transmitting member hinged to said piston in sucha way as to permit relative movement between said piston and said forcetransmitting member, conduit means extending from the end of the pistonadjacent said force transmitting member and communicating with theexterior of the piston, means to supply oil under pressure to said forcetransmitting member and valving means controlled by relative movementbetween said piston and said force transmitting member for controllingthe flow of pressure oil into said conduit means, the conduit meanscomprising an axial bore in the piston and a rod pressed into said borein the piston together with conduit grooves formed at the junction ofthe rod and bore.

2. A hydrostatic power unit of the type having a piston reciprocating ina cylinder and a force transmitting member hinged to said piston in sucha way as to penmit relative movement between said piston and said forcetransmitting member, conduit means extending from (the end of the pistonadjacent said force transmitting member and communicating with theexterior of the piston, means to supply oil under pressure to said forcetransmitting member and valving means controlled by relative movementbetween said piston and said force transmitting member for controllingthe flow of pressure oil into said conduit means, the conduit meanscomprising an axial bore in the piston and a rod pressed into said borein the piston, said rod being formed with conduit grooves on its outersurface.

3. A hydrostatic power unit of the type having a piston reciprocating ina cylinder and a force transmitting member hinged to said piston in sucha way as to permit relative movement between said piston and said forcetransmitting member, conduit means extending from the end of the pistonadjacent said force transmitting member and communicating with theexterior 'of the piston, means to supply :oil under pressure to saidforce transmitting member and valving means controlled by relativemovement between said piston and said force transmitting member forcontrolling the flow of pressure oil into said conduit means, theconduit means comprising an axial bore in the piston and a rod pressedinto said bore in the piston, said rod being formed with helical conduitgrooves on its outer surface.

4. A hydrostatic power unit of the type having a piston reciprocating ina cylinder and a shoe hinged to said piston in such a way as to permitrelative rocking movement between said piston and said shoe, a pluralityof generally radial ducts in said piston near the central portion of thepiston and extending to the exterior thereof, the same plurality ofgenerally radial ducts in said piston located near the inner end of saidpiston and extending to the exterior thereof, the same plurality ofconduits extending from the end of the piston adjacent to said shoe andeach communicating with one of said first mentioned ducts, and thenextending to and communicating with that one of said second mentionedgenerally radial ducts which is on the opposite side of the piston fromthe said first mentioned duct, means to supply oil under pressure tosaid shoe and valving means controlled by relative rocking movementbetween said piston and said shoe for controlling the flow of pressureoil into said conduits.

5. The combination according to claim 4 in which that part of theconduits extending from the first ducts to the second duets constitutepart of a helix.

6. The combination according to claim 4 in which the conduits are formedas a helix making a half turn from the shoe to the first ducts and 'asecond half turn from the first ducts to the second ducts.

7. The combination according to claim 4 in which the conduits are formedas a helix making a half turn from the shoe to the first ducts and asecond half turn from the first ducts to the second ducts, and in whichthe distance fnom the shoe to the first ducts is the same as from thefirst ducts to the second ducts.

8'. A hydrostatic power unit of the type having a piston reciprocatingin a cylinder and a shoe spherically hinged to said piston in such a wayas to permit relative movement between said piston and said shoe, aplurality of conduits extending from the end of the piston adjacent tosaid shoe and opening at points equally spaced from the axis of thepiston and each communicating with the exterior of the piston, acircular pocket formed in the spherical surface of the shoe whichcontacts with the spherical part of the piston, which pocket is of adifferent radius than the radius of the locations of the openings of theconduits in the spherical piston surface but connecting with at leastone of said conduits when the shoe is tilted relative to the piston, andmeans to supply oil under pressure to said pocket, whereby the supply ofoil to said conduits is controlled by relative movement between saidpiston and said shoe, the radius of the pocket being smaller than theradius of the locations of the openings of the conduits in the sphericalpiston surface and the conduits being so formed that each conduit opensat the exterior of the piston at a point on the opposite side of thepiston axis from the point at which it starts in the spherical pistonsurface.

9. A hydrostatic power unit of the type having a piston reciprocating ina cylinder and a shoe spherically hinged to said piston in such a way asto permit relative movement between said piston and said shoe, aplurality of conduits extending from the end of the piston adjacent tosaid shoe and opening at points equally spaced from the axis of thepiston and each communicating with the exterior of the piston, acircular annular groove formed in the spherical surface of the shoewhich contacts with the spherical part of the piston, the inner radiusof the circular annular gnoove being greater than the radius of thelocations of the openings of the conduits in the spherical piston ballsurface but connecting with at least one of said conduit openings whenthe shoe is tilted relative to the piston, and means to supply oil underpressure to said annular groove, whereby the supply of oil to saidconduits is controlled by relative movethem between said piston and saidshoe, the conduits being so formed that each conduit opens at theexterior of the piston at a point on the same side of the piston ballaxis as that from which it starts in the spherical piston surface.

10. A hydrostatic power unit of the type having a piston reciprocatingin a cylinder and a force transmitting member hinged to said piston insuch a way as to permit relative movement between said piston and saidforce transmitting member, conduit means extending from the end of thepiston adjacent said force transmitting member and communicating withthe exterior of the piston, an oil passage extending from the inner endof said piston to the outer end thereof adjacent to said forcetransmitting member and serving to supply oil under pressure to saidforce transmitting member and valving means controlled by relativemovement between said piston and said force transmitting member forcontrolling the flow of pressure oil into said conduit means, the saidoil passage extending from the inner end of the piston to the outer endthereof comprising at least one generally radial duct near the inner endof the piston connected to the space between the cylinder wall and thepiston and serving to conduct oil from said space to an axial passage inthe piston which extends to the outer end thereof.

11. A hydrostatic power unit of the type having a piston reciprocable ina cylinder and formed with a ball at its outer end and a shoe having aspherical socket embracing said ball, so that said shoe is hinged tosaid piston to permit universal relative rocking movement between saidpiston and said shoe, a plurality of conduits extending from the ballend of the piston from points equally spaced from the axis of the pistonand communicating with the exterior of the piston, an oil passageextending from the inner end of said piston to the outer end thereof andserving to supply oil under pressure to a circular pocket formed in thespherical socket in said shoe, said pocket being so formed, located anddimensioned as to form a connection to at least one of said conduitswhen said shoe is tilted, whereby the oil supply to said conduits iscontrolled by tilting movement between said ball ended piston and saidspherical socket in said shoe.

12. A hydrostatic power unit of the type having a piston reciprocable ina cylinder and formed with a ball at its outer end and a shoe having aspherical socket embracing said ball, so that said shoe is hinged tosaid piston to permit universal relative rocking movement between saidpiston and said shoe, a plurality of conduits extending from the ballend of the piston from points equally spaced from the axis of the pistonand communicating with the exterior of the piston, an oil passageextending from the inner end of said piston to the outer end thereof andserving to supply oil under pressure to a circular pocket formed in thespherical socket in said shoe, said pocket being so formed, located anddimensioned as to form a connection to at least one of said conduitswhen said shoe is tilted, whereby the oil supply to said conduits iscontrolled by tilting movement between said ball ended piston and saidspherical socket in said shoe, the pocket in the spherical socket insaid shoe comprising a circular groove whose inner radius is larger thanthe radius of the locations of the openings of the conduits in the ball,and the conduits being so formed that each conduit opens at the exteriorof the piston at a point on the same side of the piston axis as thatfrom which it starts in the spherical piston ball surface.

13. A hydrostatic power unit of the type having a piston reciprocable ina cylinder and formed with a ball at its outer end and a shoe having aspherical socket embracing said ball, so that said shoe is hinged tosaid piston to permit universal relative rocking movement between saidpiston and said shoe, a plurality of conduits extending from the ballend of the piston from points equally spaced from the axis of the pistonand communicating with the exterior of the piston, an oil passageextending from the inner end of said piston to the outer end thereof andserving to supply oil under pressure to a circular pocket formed in thespherical socket in said shoe, said pocket being so formed, located anddimensioned as to form a connection to at least one of said conduitswhen said shoe is tilted, whereby the oil supply to said conduits iscontrolled by tilting movement between said ball ended piston and saidspherical socket in said shoe, the radius of the pocket being smallerthan the radius of the locations of the openings of the conduits in thespherical piston ball surface and the conduits being so formed that eachconduit opens at the exterior of the piston at a point on the oppositeside of the piston axis from the point at which it starts in thespherical piston ball surface.

References Cited in the file of this patent UNITED STATES PATENTS1,274,391 Davis Aug. 6, 1918 2,300,009 Rose Oct. 27, 1942 2,518,619Huber Aug. 15, 1950 2,699,123 Bonnettee et al Jan. 11, 1955 2,735,407Born Feb. 21, 1956 2,847,938 Gondlek Aug. 9, 1958 2,968,287 CreightonJan. 17, 1961 FOREIGN PATENTS 293,506 Great Britain July 12, 1928883,348 France Mar. 22, 1943 1,132,634 France Mar. 13,1957

1. A HYDROSTATIC POWER UNIT OF THE TYPE HAVING A PISTON RECIPROCTING INA CYLINDER AND A FORCE TRANSMITTING MEMBER HINGED TO SAID PISTON IN SUCHA WAY AS TO PERMIT RELATIVE MOVEMENT BETWEEN SAID PISTON AND SAID FORCETRANSMITTING MEMBER, CONDUIT MEANS EXTENDING FROM THE END OF THE PISTONADJACENT AND FORCE TRANSMITTING MEMBER AND COMMUNICATING WITH EXTERIOROF THE PISTON, MEANS TO SUPPLY OIL UNDER PRESSURE TO SAID FORCETRANSMITTING MEMBER AND VALVING MEANS CONTROLLED BY RELATIVELY MOVEMENTBETWEEN SAID PISTON AND SAID FORCE TRANSMITTING MEMBER FOR CONTROLLINGTHE FLOW OF PRESSURE OIL INTO SAID CONDUIT MEANS, THE CONDUIT MEANSCOMPRISING AN AXIAL BORE IN THE PISTON AND A ROD PRESSED INTO SAID BOREIN THE PISTON TO-